1. Field of the Invention
The present invention relates to an electronic device and a method of manufacturing the same, especially to an electronic device in which a circuit chip is mounted on a film-shaped base body and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, there has been widely known an electronic device in which a circuit chip is mounted on a base such as a printed circuit board. Such an electronic device is built in an electronic equipment to control the electronic equipment, or used alone to exchange information with external equipment. Such an electronic device includes Radio Frequency Identification (RFID) tags of various kinds that wirelessly exchange information in a non-contact manner with an external device typified by a reader/writer. One type of RFID tag that has been proposed has a structure in which a conductor pattern for radio communication and an IC chip are mounted on a sheet-like base. Applications of such an RFID tag include identification of an article by attaching the RFID tag to the article and thereby exchanging information about the article with external equipment.
Incidentally, there is the demand for a more compact and lighter RFID. Specifically, a thinner and more flexible RFID with decreased cost is demanded. In response to such a demand, there has been proposed a RFID tag in which a film formed of a resin material such as polyethylene terephthalate (PET) is used as a base on which an IC chip is mounted (See Japanese Patent Application Laid-open No. 2001-156110, for example).
FIG. 10 is a drawing for explaining a conventional method of manufacturing a RFID tag.
In Part (a) to Part (d) of FIG. 10, each step for manufacturing a RFID tag is sequentially shown.
To manufacture a RFID tag, firstly, as shown in Part (a) of FIG. 10, a base body 91 composed of a film 911 made of the PET and a conductive pattern 912 formed on the film 911 that functions as an antenna of the RFID tag is prepared, and a thermosetting adhesive 93p that hardens by heating is adhered to the base body 91.
Next, as shown in Part (b) of FIG. 10, an IC chip 92 is placed on a portion of the base body 91 where the thermosetting adhesive 93p is adhered to. On the IC chip 92, bumps 921 connected to the conductive pattern 912 have been formed. As shown in Part (c) of FIG. 10, the IC chip 92 is placed on the base body 91 in such a way that the bumps 921 are aligned with the conductive pattern 912.
Next, as shown in Part (d) of FIG. 10, the base body 91 mounted with the IC chip 92 is pinched by a heating device 8 so as to be pressed on the IC chip 92 side (one side of the base body 91 where the IC chip 92 is mounted) and on a film 911 side (the other side of the base body 91 where the film 911 is disposed). The heating device 8 includes a heating head 81 that abuts the IC chip 92 and a heating stage 82 that abuts to support the base body 91. Then, the thermosetting adhesive 93p is hardened through the application of heat by the heating head 81 of the heating device 8. In this way, the IC chip 92 is fixed to the base body 91 in a state where the bumps 921 contact the conductive pattern 912, which completes a compact and lightweight RFID tag.
However, PET material that forms the film 911 is low in heat resistance as it has the glass transition temperature of about 67° C. Therefore, the film 911 is likely to deform when the thermosetting adhesive 93p is heated and hardened.
FIG. 11 is a diagram for explaining a state of the base body in the step of heating in Part (d) of FIG. 10.
As shown in Part (a) of FIG. 11, if the processing of heating is executed in a condition where the IC chip 92 is placed on the base body 91, the temperature of the base body 91 rises and as shown in Part (b) of FIG. 11, the film 911 becomes deformed. If the thermosetting adhesive 93p in the middle of hardening flows due to the deformation of the film 911, then air bubbles are generated in the thermosetting adhesive 93p and remain as voids 931 after the hardening is completed. As the voids in the solidified thermosetting adhesive 93p lowers the adhesion between the IC chip 92 and the base body 91, the reliability of RFID tags deteriorates.
A problem of degraded reliability due to the generation of voids like this is not limited to RFID tags but common to electronic devices in which a circuit chip is mounted on a film-shaped base body.